The disclosures herein relate generally to flexible leaflet prosthetic heart valves and more particularly to wire stents used to reinforce the valves.
Wire stents used in prosthetic heart valves are normally symmetrical in geometry, with all belly radii being equal. When a stent flat pattern is formed and joined, a crimp collar is used to join the wire ends. This results in a stiffened section between two of the adjacent posts. The stiffened section causes an imbalance in the stress levels between the various posts when equal forces are applied at the post tips, or along the posts, due to loads being experienced by the leaflet members. For example, a post opposite the crimp collar will deflect more than the posts which are adjacent the crimp collar. As a result, the difference in post deflections may affect performance and durability of the prosthetic valve leaflets.
Various stented valve devices have been proposed. U.S. Pat. No. 4,106,129 discloses a supported bioprosthetic heart valve in which the supporting stent is capable of annular deformation and also of limited perimetric expansion and contraction during heart operation. The stent includes a wire frame composed of a single flexible wire preformed to define inverted U-shaped commissure supports merging smoothly with arcuate portions connecting such supports. This device does not address the relationship between belly radii symmetry and balanced stent post deflections.
In U.S. Pat. No. 4,343,048, a stent for a cardiac valve comprises a base ring having metal legs projecting therefrom in a generally axial direction, each leg being flexible in such a manner that, when the stent has a valve installed therein and the valve is under pressure such as when operating in the heart, each respective leg can resiliently deform over substantially its whole axial length to take up strain in the valve without impairing its performance.
U.S. Pat. No. 4,501,030 discloses a prosthetic heart valve including a frame having a plurality of commissure supports, a plurality of resilient supports, and a plurality of valve leaflets. The valve leaflets are attached to the resilient supports, and the resilient supports lie radially outwardly of the commissure supports, respectively. When in use, the valve is subjected to forces which are used to clamp the valve leaflets between the resilient supports and the commissure supports to augment whatever other leaflet attachment techniques may be used. This device moves the crimp collar from the belly region to a location in the stent post area, but does not address the stent post deflection balance as a function of the belly radii. Unfortunately, known devices using wire stents have not addressed the above-mentioned imbalance condition created by the use of crimp collars.
U.S. Pat. No. 5,037,434 discloses a bioprosthetic heart valve comprising first and second mechanisms for supporting leaflets to provide multiple effective spring constants. An inner frame supporting commissures of the valve is elastic, permitting the commissures to bend in toward the center of the prosthetic heart valve at very low loads. A relatively rigid annular support ring supports the elastic frame and provides the second spring constant mechanism. An attachment system for sewing bioprosthetic leaflets to the frame and clamping the leaflets between the frame and the annular ring minimizes stress risers in the leaflets. The leaflets have an uncoupled mating edge where the leaflets meet in the center of the valve. The uncoupled portions of the leaflets permit the leaflets to roll by each other.
U.S. Pat. No. 5,545,215 discloses a frame to be placed as an external support of a biological valved conduit containing three leaflets. This external frame, made of biocompatible metal or plastic is sutured to the outer surface of the valved conduit made of biological or biocompatible membrane or sigmoid valve root in order to maintain its natural geometry. The frame has a general cylindrical configuration, circular as viewed from above and below. From a side view however, both upper and lower ends of the cylinder present three convex curvatures joined at equidistant points of the circumference. These upper and lower curves are joined by three vertical struts, so that three large saddle shaped paraboloid gaps result. The frame is a wire-like structure.
U.S. Pat. No. 5,562,729 discloses a multi-leaflet heart valve composed of biocompatible polymer which simultaneously imitates the structure and dynamics of biological heart valves. The valve includes a plurality of flexible leaflets dip cast on a mandrel. The leaflets are then bonded with a bonding agent to the interior surfaces of a plurality of struts on a metal-reinforced prosthetic stent. The leaflets open and close in response to the pumping action of the heart.
Some manufacturers of wire stented valves have ignored the imbalance problem. Others have taken approaches which do not address stent post deflection balance as a function of belly radii. Therefore, what is needed is a wire stented valve which compensates for the imbalance caused by crimp collars.